Kenwood ka-405

mikecheryl10

KENWOOD KA-405
Hi Everyone!!

Help Help i need to fix my kenny Ka-405, which has been blowing both the fuses. I happened to open it up to fix the distortion on the left channel and clean the entire amp. I had removed the output transistor and In hurry fixed the two output transistors at the wrong place, since then the fuse has been blowing, please if could some one help me in getting back to life this amplifier.

Any help will be appreciated :drool:
 
Pull the output transistors and test them. Probably should test the drivers and check the emitter resistors for the drivers and the outputs as well. Do not attempt to replace any more fuses and power up without using a dim-bulb tester (search here or on Google for more info on the DBT).

Problem with the 405 is the oddball outputs that it uses...it may be a real PITA to locate them, and might be easier to sub in some modern device (which may mean drilling and tapping the heasink for new mounting holes).
 
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thanks for the advise I will check the output transistors, but could you id me the driver transistors and and the emitter ressistor, cause i am still learning about electronics. I have sm downloaded. thanks in advance
 
The crappy download I have is hard to read. Probably the same thing you have. If you're serious about tackling this project, I strongly suggest you contact Rick at Stereomanuals.com and order up something readable.

At any rate, it looks like the drivers (for the L channel...you can deduce the ones for the R channel) are Q15 & Q17. There's also a diode (D7) and the R41 emitter resistor, as well as the R47 & R49 emitter resistors. All these are suspect.
 
That the pre-driver (Q13, Q14) is likely toast.

Cross your fingers that D5 survived...it is a rare part.
 
Cross that bridge when you come to it. Need to find out if the one you have is good first.
 
Its friday and day off for me, I live in Kuwait. I ran a check on the suspected components which you pointed at and some around it. Replaced all the fried ressistors. The following parts were found faulty apart from what you pin pointed D1,6,15 & Q16,18. The D5 turned out to be fine. I am having a problem in finding the diodes and transistors here, can you please advise where will i get all these parts and how much will it cost me. Thanks in advance.....
 
D1 & D15 are 1/2W 14V zener diodes (1N5244B), available anywhere electronics are sold . D6 is the STV-4H multijunction diode, and might be had from Pioneer parts, search for 'STV4'.

Q16 can be replaced with the Fairchild KSC2690 or the KSC2690A, and Q18 replaced with the Fairchild KSA1220 or the KSA1220A. But because of your location, I cannot suggest where you might be able to purchase these parts. In the US, Mouser sells all except the STV4 diode.
 
The list of transistors with that mounting pattern is a short one, and not one that I have compiled. Like I said earlier, if I had one in front of me with dead outputs, I'd probably find a way to shoehorn in some modern device, which would likely mean drilling and tapping the heatsink to accommodate them.
 
Hi EW, its been a long time, i have managed to get most of the parts and have replaced all the suspects except the output transisitors. The output transistors are removed out from the board. Hopefully I should be receving the replacement in a day or two. I have a question. What if I power the amp without the output transistors will the relay click, ofcourse I will be using DBT as suggested by you, just to be sure that the ciruit is correct before adding the Output Transistor. Thanks in advance...
 
The driver stage is not tied to the output line, therefore there's no feedback and the amp will not come out of protection. You need those outputs in the amp before you apply power. Hopefully you have also built a dim-bulb tester, as I suggested a while back. A 100W bulb would be a good one to use and will tell you if there's some major issue you have overlooked.
 
THANKS EW. I PLACED ALL THE PARTS ON THE CIRUIT AND POWERED IT UP USING THE DIM-BULB TESTER USING A 100 WATTS BULB, THE BULB DIDN'T LITE UP AT ALL, NOR DID THE AMP CAME OUT OF PROTECTION. I CHECKED THE VOLTAGE AFTER RECTIFING AND SMOOTHENING +35 AND -35 VOLTS. BUT AT Q19 BASE -45 COLLECTER -46 ABD EMMITER -45 / Q22 BASE -45 COLLECTER +45 EMMITER -45/Q21 EMITTER -45.5 COLLECT +46.6 BASE -45/ Q 20 EMIITER -45 COLLECTER -45 BASE -45.6 WHICH SEEMED TO BE WIERD.

FOLLOWING PARTS WERE SUBSITUTED
Q17,18 WITH BD138
Q15,16 WITH BD 139
Q19,20 WITH 2SC2837
Q21,22 WITH 2A11186
D12,15,6 WITH ZENEER DIODE 13V 1/2 WATT AS 14V WAS NOT AVAILABLE.

PLEASE ADVISE WHERE SHOULD I BE LOOKING TO TRACE THE PROBLEM.

sHOULD I BE SHORTING D5,6 TO GET THE AMP OUT OF PROTECTION.

THANKS FOR GUIDING ME
 
Your 100W lamp should have at least lit up briefly as the large power supply caps charged...how is it wired?

The BD138 and 139 are not rated for the kind of circuit you have...the originals were 100V parts, and the 138 & 139 are only rated for 60V. You need something better here.

So both channels are showing -45V at their output?

Shorting D5 or D6 will not bring the amp out of protection. Did you test these diodes?
 
I will surely get bd 138 /139 replaced to something rated 100v
Everything is showing approximate -45V at the output except Q21 collector/q22 collector is showing +45V.

D5,D6 diode test was showing correct.
 
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